When virus infects the body, the proliferation of the virus in the infected cells occurs, and the proliferated virus particles bud out through the cell membrane to infect other surrounding cells. In part of the defense mechanism of cells against viral infection, Bst-2 tetherin) protein is expressed in the cell membrane. The Bst-2 protein has cell membrane-binding sites at both the N-terminus and the C-terminus, and thus is expressed in the cell membrane in a form in which the middle is lifted, like a bridge. The C-terminus of Bst-2 is located in the lipid raft region of the cell membrane, which is a specific region in which receptor activation occurs, and the N-terminus is located in the non-lipid raft region. When virus buds from the lipid raft region to the outside of the cells, the Bst-2 protein inhibits the passage of virus particles through the cell membrane by its region fixed to the non-lipid raft region. For this defense mechanism of mammal cells, some viruses produce a protein that promotes the degradation of the Bst-2 protein in order to avoid this mechanism of the host cells. This paradoxically indicates that the function of the Bst-2 gene strongly contributes to the inhibition of production of virus.
Until now, for the production of viruses for producing vaccines, a method of inoculating seed virus into fertilized eggs and culturing the inoculated virus has been used (KR 2012-0103737A). However, this method has very low efficiency due to problems, including allergic induction, the security of supply of fertilized eggs, and viral propagation. In an attempt to overcome such problems, methods of producing viral vaccines by animal cell culture have been used (KR 2012-0033334A). These methods include a method of producing a vaccine by culturing a large amount of animal cells under germ-free conditions and infecting the cultured animal cells with virus, a method of producing only antigens, which induce the production of antibodies against pathogens, by a genetic engineering method, etc. The biggest advantage of the method of producing vaccines by animal cell culture is that the production scale can be expanded. Specifically, the production scale can be expanded as desired according to the culture scale of animal cells that are used as a raw material for vaccine production.
However, despite such many advantages, the production of vaccines by animal cell culture is not easy to achieve. This is because the yield per unit volume is somewhat lower. In order to overcome low yields per unit volume when producing vaccines using animal cells, there were some attempts to develop excellent host animal cell lines using genetic engineering techniques (Jang J. et al., Appl. Microbiol. Biotechnol 85:1509-1520, 2010), but such attempts still remain at an insufficient level. Thus, to optimize virus production, the identification of a virus-producing cell line, the improvement of culture conditions and the improvement of infection conditions are required.
In previous studies, the present inventors found that when the function of Bst2 gene in a cell line having an ability to produce virus is lost, the release of the virus from the cell line is promoted so that the ability to produce the virus increases, and the apoptosis of the host cell is inhibited so that the stability of the virus-producing cell line increases (WO 2014142433).
Accordingly, the present inventors have made extensive efforts to find optimal methods for the production of virus and the production of a viral antigenic protein by improving the production yield of a target virus for producing a vaccine using an animal cell line, and as a result, have found that, if Bst2 protein in an animal cell line is removed, the release of virus from the animal cell line will be promoted, the apoptosis of the host cell will be inhibited, the viral infection of the host cell will be significantly promoted, and the production of a target virus will be increased, thereby completing the present invention.